Back to EveryPatent.com
United States Patent |
6,107,234
|
Bortinger
|
August 22, 2000
|
Phosphorus/vanadium maleic anhydride catalyst preparation
Abstract
A VPO catalyst precursor having the formula (VO)HPO.sub.4 aH.sub.2 OM.sub.m
P.sub.p O.sub.y wherein M is at least one promoter element selected from
the group consisting of elements from Groups IA, IB, IIA, IIIA, IIIB, IVA,
IVB, VA, VB, VIA, VIB, and VIIIA of the Periodic Table of the Elements,
and mixtures thereof, a is a number of at least about 0.3, m is a number
of from about 0 to about 0.3, p is a number of from about 0 to about 0.3,
any y corresponds to the amount of oxygen necessary to satisfy the valence
requirements of all elements present, is activated by heating the catalyst
precursor in an atmosphere selected from the group consisting of air,
steam, inert gas, and mixtures thereof to a temperature not to exceed
about 300.degree. C., maintaining the catalyst precursor at this
temperature and providing an atmosphere containing molecular oxygen,
steam, and optionally an inert gas, increasing the temperature at a
programmed rate of from about 0.5.degree. C./min to about 15.degree.
C./min to a value effective to eliminate the water of hydration from the
catalyst precursor, adjusting the temperature to a value greater than
350.degree. C., but less than 550.degree. C., and maintaining the adjusted
temperature in a molecular oxygen/steam-containing atmosphere comprised of
at least 1 vol % oxygen for a time effective to provide a vanadium
oxidation state of from about +4.0 to about +4.5 and to complete
transformation of the precursor to the active catalyst having the Formula
(VO).sub.2 P.sub.2 O.sub.7 M.sub.2m P.sub.2p O.sub.y wherein M, m, p and y
are defined above.
Inventors:
|
Bortinger; Arie (Ridgewood, NJ)
|
Assignee:
|
Scientific Design Company, Inc. (Little Ferry, NJ)
|
Appl. No.:
|
239651 |
Filed:
|
January 29, 1999 |
Current U.S. Class: |
502/209; 502/210; 502/211; 502/212 |
Intern'l Class: |
B01J 027/198; B01J 027/188; B01J 027/19; B01J 027/192 |
Field of Search: |
502/209-212
|
References Cited
U.S. Patent Documents
3980585 | Sep., 1976 | Kerr et al. | 252/437.
|
4043943 | Aug., 1977 | Schneider | 252/437.
|
4056487 | Nov., 1977 | Kerr | 252/435.
|
4147661 | Apr., 1979 | Higgins et al. | 252/435.
|
4283307 | Aug., 1981 | Barone et al. | 252/432.
|
4418003 | Nov., 1983 | Udovich et al. | 502/209.
|
4515904 | May., 1985 | Edwards | 502/209.
|
4569925 | Feb., 1986 | Yang et al. | 502/209.
|
5137860 | Aug., 1992 | Ebner et al. | 502/209.
|
5280003 | Jan., 1994 | Bortinger | 502/209.
|
5288880 | Feb., 1994 | Matsuura | 549/260.
|
5296436 | Mar., 1994 | Bortinger | 502/209.
|
5480853 | Jan., 1996 | Bortinger | 502/209.
|
5496787 | Mar., 1996 | Hatano et al. | 502/209.
|
5510308 | Apr., 1996 | Kourtakis | 502/209.
|
5847163 | Dec., 1998 | Mazzoni et al. | 549/243.
|
5885919 | Mar., 1999 | Bortinger | 502/209.
|
5922637 | Jul., 1999 | Bortinger | 502/209.
|
5945368 | Aug., 1999 | Felthouse et al. | 502/209.
|
Other References
Applied Catalysts 72 (1991) 1-32, Graham J. Hutchings, "Effect of promoters
and reactant concentration on the selective oxidation of n-butane to
maleic anhydride using vanadium phosphorus oxide catalysts" Sep. 1990.
|
Primary Examiner: Bell; Mark L.
Assistant Examiner: Hailey; Patricia L.
Attorney, Agent or Firm: Long; William C.
Claims
What is claimed is:
1. The process for activating VPO maleic anhydride catalyst precursor
having the formula (VO)HPO.sub.4 aH.sub.2 OM.sub.m P.sub.p O.sub.y wherein
M is at least one promoter element selected from the group consisting of
elements from Groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA,
VIB, and VIIIA of the Periodic Table of the Elements, and mixtures
thereof, a is a number of at least about 0.3, m is a number of from about
0 to about 0.3, p is a number of from about 0 to about 0.3, any y
corresponds to the amount of oxygen necessary to satisfy the valence
requirements of all elements present which comprises heating the catalyst
precursor in an atmosphere selected from the group consisting of air,
steam, inert gas, and mixtures thereof to a temperature not to exceed
about 300.degree. C., maintaining the catalyst precursor at this
temperature and providing an atmosphere containing molecular oxygen,
steam, and optionally an inert gas, increasing the temperature at a rate
of from about 0.5.degree. C./min to about 15.degree. C./min to a value
effective to eliminate the water of hydration from the catalyst precursor,
adjusting the temperature to a value greater that 350.degree. C., but less
than 550.degree. C., and maintaining the adjusted temperature in a
molecular oxygen/steam-containing atmosphere comprised of at least 1 vol %
oxygen for a time effective to provide a vanadium oxidation state of from
about +4.0 to about +4.5 and to complete transformation to the active
catalyst having the formula (VO).sub.2 P.sub.2 O.sub.7 M.sub.2m P.sub.2p
O.sub.y wherein M, m, p and y as defined above.
2. The process of claim 1 wherein the said molecular
oxygen/steam-containing atmosphere is comprised of at least 2 vol %
oxygen.
3. The process of claim 1 wherein the said molecular
oxygen/steam-containing atmosphere is comprised of 3-8 vol % oxygen.
4. The process for activating VPO maleic anhydride catalyst precursor
formed by reduction of pentavalent vanadium in the presence of a dialkyl
sulfoxide, said precursor having the formula (VO)HPO.sub.4 aH.sub.2
OM.sub.m P.sub.p O.sub.y wherein M is at least one promoter element
selected from the group consisting of elements from Groups IA, IB, IIA,
IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIB, and VIIIA of the Periodic
Table of the Elements, and mixtures thereof, a is a number of at least
about 0.3, m is a number of from about 0 to about 0.3, p is a number of
from about 0 to about 0.3, any y corresponds to the amount of oxygen
necessary to satisfy the valence requirements of all elements present
which comprises heating the catalyst precursor in an atmosphere selected
from the group consisting of air, steam, inert gas, and mixtures thereof
to a temperature not to exceed about 300.degree. C., maintaining the
catalyst precursor at this temperature and providing an atmosphere
containing molecular oxygen, steam, and optionally an inert gas,
increasing the temperature at a rate of from about 0.5.degree. C./min to
about 15.degree. C./min to a value effective to eliminate the water of
hydration from the catalyst precursor, adjusting the temperature to a
value greater that 350.degree. C., but less than 550.degree. C., and
maintaining the adjusted temperature in a molecular
oxygen/steam-containing atmosphere comprised of at least 1 vol % oxygen
for a time effective to provide a vanadium oxidation state of from about
+4.0 to about +4.5 and to complete transformation to the active catalyst
having the formula (VO).sub.2 P.sub.2 O.sub.7 M.sub.2m P.sub.2p O.sub.y
wherein M, m, p and y as defined above.
5. The process of claim 4 wherein the catalyst precursor is formed by
reduction of pentavalent vanadium in the presence of dimethyl sulfoxide.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved method for the preparation of
active vanadium/phosphorus mixed oxide catalysts which have special
utility in the production of maleic anhydride.
2. Description of the Prior Art
Catalysts containing vanadium and phosphorus oxides have been used in the
oxidation of 4-carbon atom hydrocarbons, such as n-butane, with molecular
oxygen or oxygen containing gas to produce maleic anhydride. Conventional
methods of preparing these catalysts involve reducing a pentavalent
vanadium compound, and if desired, promoter element compounds under
conditions which will provide or maintain vanadium in a valence state
below +5 to form catalyst precursors which are recovered and converted to
active catalyst.
U.S. Pat. No. 5,137,860 provides a comprehensive description of the prior
art in this area. The patent shows the use of organic reducing agents as
well as hydrogen chloride and teaches the use of activation procedures
whereby the catalyst precursor is contacted at prescribed conditions with
oxygen and steam mixtures and finally with a non-oxidizing steam
atmosphere to produce an active catalyst.
U.S. Pat. No. 4,569,925 describes the preparation of vanadium/phosphorus
mixed oxide catalysts by an organic solution method using anhydrous
hydrogen chloride as an agent for the solubilization of the vanadium
component, and teaches an activation procedure whereby the catalyst
precursor is contacted not with air alone but with a mixture of air and a
hydrocarbon such as methane, ethane, propane, butane and the like.
The synthesis of VPO catalysts can be carried out both in aqueous and in
organic solvent media. Anhydrous conditions are preferred in the organic
solvent method, and the synthesis in organic solvents is presently the
preferred method due to the better performance of the catalyst. This is
attributed to greater surface areas of the catalyst when prepared in
organic solvent than in aqueous media (G. J. Hutchings, Applied Catalysis,
72(1991), 1-32 and references therein).
In the organic solvent method typically employing isobutanol, anhydrous HCl
has been used as reducing agent for the V.sub.2 O.sub.5. Other reducing
agents have been used such as oxalic acid or organic alcohols such as
allyl alcohol, benzyl alcohol and isobutanol which can be both the solvent
and reducing agent. With HCl, the V.sub.2 O.sub.5 is converted to an IBA
(isobutyl alcohol) soluble material (VOCl.sub.2) prior to the addition of
phosphoric acid. In the absence of HCl, the V.sub.2 O.sub.5 is not
solubilized and the formation of the VPO catalyst is done heterogeneously
on the suspended V.sub.2 O.sub.5 in the organic solvent. The use of HCl
has produced excellent catalysts but the residual chloride in the catalyst
results in a chloride release during catalyst activation which is
undesirable. This difficulty can be overcome by removing the chlorides
through an additional step during the catalyst manufacturing.
An especially advantageous method for preparing a VPO catalyst for use in
the production of maleic anhydride is described in copending application
Ser. No. 09/108,223 filed Jul. 1, 1998, now U.S. Pat. No. 5,885,919,
wherein the catalyst is prepared in an organic solvent procedure which
involves the use of an additive such as dimethyl sulfoxide; especially
good results are achieved where a bismuth catalyst promoter is also
employed.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with the present invention, a new and improved VPO mixed
oxide catalyst activation procedure is provided whereby the VPO catalyst
precursor, which can be formed by known procedures, is converted to the
active catalyst form; the activation procedure comprises first heating the
catalyst precursor in an atmosphere selected from the group consisting of
air, steam, inert gas, and mixtures thereof to a temperature not to exceed
about 300.degree. C., maintaining the catalyst precursor at this
temperature and providing an atmosphere containing molecular oxygen,
steam, and optionally an inert gas, increasing the temperature at a
programmed rate of from about 0.5.degree. C./min to about 15.degree.
C./min to a value effective to eliminate the water of hydration from the
catalyst precursor, adjusting the temperature to a value greater than
350.degree. C., but less than 550.degree. C., and maintaining the adjusted
temperature in a molecular oxygen/steam-containing atmosphere comprised of
at least 1 vol % oxygen for a time effective to provide a vanadium
oxidation state of from about +4.0 to about +4.5 and for the
transformation of the precursor to the active catalyst.
DETAILED DESCRIPTION OF THE INVENTION
The VPO catalyst precursors which are converted to the active catalyst form
in accordance with the invention are prepared by known procedures such as
are illustratively shown in said copending application Ser. No. 09/108,223
filed Jul. 1, 1998, or in U.S. Pat. No. 5,137,860, or by other
non-corrosive preparations using the organic solvent method to prepare VPO
catalyst precursors.
In accordance with the present invention, precursors are converted to the
active catalyst form by first heating the precursor to a temperature not
to exceed about 300.degree. C. under an atmosphere of air, steam, inert
gas, or mixtures. The precursors are maintained at this temperature and an
atmosphere containing molecular oxygen, steam and optionally an inert gas
is provided, the atmosphere being generally represented by the formula
(O.sub.2).sub.x (H.sub.2 O).sub.y (IG).sub.z wherein IG is an inert gas
and x, y, and z represent mol percent of the O.sub.2, H.sub.2 O, and IG
components, respectively, in the molecular oxygen/steam-containing
atmosphere, with x having a value greater than zero (0) mol %, but less
than 100 mol %, y having a value greater than zero (0) mol %, but less
than 100 mol %, and z having a value representing the balance of the
molecular oxygen/steam-containing atmosphere. The temperature is then
increased at a programmed rate of from about 0.5.degree. C./min to about
15.degree. C./min to a value effective to eliminate the water of hydration
from the catalyst precursor while minimizing the exotherm of the catalyst
bed. Finally the temperature is adjusted to a value greater than
350.degree. C., but less than 550.degree. C., and the catalyst is
maintained at the adjusted temperature in a molecular
oxygen/steam-containing atmosphere containing more than 1 vol %,
preferably more than 2 vol % and most desirably 3-8 vol % oxygen for a
time effective to provide a vanadium oxidation state of from about +4.0 to
about +4.5 and to complete transformation of the precursor to the
activated catalyst. The atmosphere throughout the procedure can also
comprise inert gas such as nitrogen, argon, helium, carbon dioxide and the
like.
The activation procedure can be carried out at essentially atmospheric
pressure or at elevated pressure.
Generally speaking, the activation procedure of the invention results in
the transformation of a catalyst precursor represented by the formula
(VO)HPO.sub.4 aH.sub.2 OM.sub.m P.sub.p O.sub.y wherein M is at least one
promoter element selected from the group consisting of elements from
Groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIB, and VIIIA
of the Periodic Table of the Elements, and mixtures thereof, a is a number
of at least about 0.3, m is a number of from about 0 to about 0.3, p is a
number of from about 0 to about 0.3, any y corresponds to the amount of
oxygen necessary to satisfy the valence requirements of all elements
present, into an active catalyst represented by the formula (VO).sub.2
P.sub.2 O.sub.7 M.sub.2m P.sub.2p O.sub.y wherein M, m, p and y are as
defined above.
Especially preferred is the method for the preparation of a
phosphorus/vanadium/oxygen catalyst which is especially useful in the
oxidation of n-butane to maleic anhydride wherein a vanadium compound in
the +5 valence state, eg. vanadium pentoxide, is reduced in an organic
medium which contains an organic sulfoxide additive which participates in
vanadium reduction, and is reacted with concentrated phosphoric acid. The
invention can be carried out in a single step, thus greatly simplifying
catalyst preparation. After formation of the catalyst precursor, the
precursor can be converted to the active form in accordance with the
current invention.
Organic sulfoxide modifying agents which are employed in the invention have
the formula:
##STR1##
wherein R and R.sub.1 are the same or different groups having 1-8 carbon
atoms selected from alkyl, substituted alkyl, aryl and substituted aryl
groups. Preferred are sulfoxides wherein each of R and R.sub.1 are alkyl
groups having 1-4 carbon atoms and especially preferred are sulfoxides
wherein each of R and R.sub.1 is an alkyl group having 1-2 carbon atoms.
dimethyl sulfoxide is preferred, other illustrative sulfoxides are methyl
ethyl sulfoxide, diethyl sulfoxide, di-isopropyl sulfoxide, di-n-butyl
sulfoxide, and the like.
The role of the organic sulfoxide in the preparation of catalyst and the
nature of the mechanism by which catalyst performance is improved are not
clearly understood. It is possible that the sulfoxide plays a role in the
oxidation/reduction reactions during the catalyst formation. When the
product is recovered there is a strong smell of a sulfur compound which is
not observed without use of organic sulfoxide and is not present in the
initial reaction mixture. Organic sulfoxide can both undergo oxidation to
the sulfone, but also possibly can be reduced to the sulfide in our
reaction mixture.
In carrying out this embodiment vanadium pentoxide in finely divided form
is added to an organic solvent medium to which is also added an effective
amount of the organic sulfoxide. Suitable solvents are alcohols known in
this art such as, for example, a primary or secondary alcohol including
methanol, ethanol, 1-propanol, 2-propanol, butanol, 2-butanol, 2,
methyl-1-propanol, 3-methyl-2-butanol, 2,2-dimethyl-1-propanol, 1-hexanol,
4-methyl-1-pentanol, 1-heptanol, 4-methyl-1-hexanol, 4-methyl-1-heptanol,
benzyl alcohol, 1,2-ethanediol, glycerol, trimethylopropane, 4-methyl,
2-pentanone, diethylene glycol and trimethylene glycol or mixtures
thereof. The alcohols can also function as reducing agents for the
vanadium +5 compound.
Generally, the organic sulfoxide is used in an amount which corresponds to
a ratio of mols sulfoxide to atoms of vanadium of 0.001 to 1 and
preferably 0.001 to 0.5 mols sulfoxide per atom of vanadium.
It is advantageous to incorporate catalyst promoters or modifiers in the
catalyst and compounds of these components can be conveniently added to
the organic solvent mixture initially or at a later stage after the
catalyst precursor has been formed. Any of the known promoters can be used
although it is especially advantageous to use a combination of Zn, Li and
Mo promoters which are conveniently added as soluble compounds to the
organic solvent. Especially outstanding results are achieved where a
bismuth promoter is used. Other promoters include those described in U.S.
Pat. Nos. 3,980,585, 4,056,487, 4,515,904, 4,147,661, 4,418,003, and the
like the disclosures of which are incorporated herein by references.
In especially preferred practice, concentrated phosphoric acid is also
added to the vanadium containing organic solvent solution which also
contains the dialkyl sulfoxide and optionally the promoter compound or
compounds, and the resulting mixture is digested at about 20 to
200.degree. C. for a period of 1 to 24 hours.
In a less preferred embodiment, the phosphoric acid can be added after the
vanadium pentoxide has been reduced in the organic solvent solution and
the resulting mixture then digested to form the catalyst precursor.
The reduction and digestion procedures are carried out to form a VPO
catalyst precursor which is represented by the formula (VO)HPO.sub.4
aH.sub.2 OM.sub.m P.sub.p O.sub.y wherein M is at least one promoter
element selected from the group consisting of elements from Groups IA, IB,
IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIB, VIB, and VIIIA of the
Periodic Table of the Elements, and mixtures thereof, a is a number of at
least about 0.3, m is a number of from about 0 to about 0.3, p is a number
of from about 0 to about 0.3, any y corresponds to the amount of oxygen
necessary to satisfy the valence requirements of all elements present.
To obtain the mixed oxides of vanadium and phosphorus, phosphoric acid of
approximately 100% H.sub.3 PO.sub.4 (98 to 101%) is added. Superphosphoric
acid (105-115%) can also be used while maintaining the desired P/V rate.
Digestion of the vanadium compound is discerned by a change in the color
of the reaction mixture to a blue color, the alcohol can be partially
stripped or not and the precursor recovered by filtration and thereafter
dried to produce the dried catalyst precursors.
The digestion of the vanadium compound in the phosphoric acid is normally
conducted at reflux in order to form the VPO precursor during this step.
The final removal of alcohol and sulfoxide or derivative if used is carried
out in a drying step in an oven at a temperature in the range of 100 to
180.degree. C. for 1-24 hours. Lower temperatures and longer times can be
used. Reduced pressure can also be applied during the drying step.
Following drying, calcination of the dried catalyst precursor is carried
out at a temperature in the range of about 200 to 300.degree. for a
sufficient period to improve the catalytic properties of the composition
and remove volatile materials, usually 1-15 hours. The catalyst powder
after the calcination step or even after the drying step is mixed with a
lubricant such as graphite and fabricated to the desired geometric shape.
Following calcination, the catalyst precursors are activated by the
procedure of the invention as described above.
Preferred catalyst precursors may contain one of more promoters including
Zn, Mo, Li, and Bi.
When Zn promoter is used, generally the atomic ratio of Zn to vanadium is
in the range of 0.001 to 0.15:1, however it has been found that lower
ratios of zinc/vanadium produce the most active catalyst and compositions
containing Zn/V mole ratio in the range of 0.01 to 0.07 are preferred.
Where lithium is used, lithium component is present at an atomic ratio of
0.001 to 0.15/1, Li/V. Where molybdenum is used, the Mo/V atomic ratio is
suitably 0.005 to 0.10, Mo/V.
Bismuth is a preferred promoter and is conveniently used in an atomic ratio
of B/V in the range 0.001 to 0.15/1, preferably 0.005 to 0.07/1.
The modifier components are added as the compound thereof such as acetates,
acetylacetonates, carbonates, chlorides, bromides, oxides, hydroxides,
phosphates and the like, e.g. a bismuth salt of an organic acid or mixture
of organic acids such as bismuth ethyl hexanoate, zinc acetyl acetonate,
zinc acetate, lithium acetate, lithium carbonate, lithium oxide, or
lithium orthophosphate and the like.
The molybdenum compound may be dissolved in an organic solvent, as
described above or water and added to the reaction mixture. The solvent
containing the molybdenum compound may be added with the other modifiers
or at different times. The use of a soluble molybdenum compound dissolved
in a solvent according to the present invention for addition to the
reaction mixture has been found to be particularly effective in dispersing
the molybdenum throughout the mixture and the final dried catalyst. Some
examples of suitable soluble molybdenum catalyst include phosphomolybdic
acid, ammonium molybdate (VI) tetrahydrate, lithium molybdate, molybdenum
tetrabromide, molybdenum trioxyhexachloride and the like.
As an essential aspect of the present invention, the catalyst precursor
formed as above indicated or by conventional procedures is activated by
the activation procedure of the present invention.
The catalyst precursor is first heated at temperatures not exceeding
300.degree. C. under an atmosphere which can be air, steam, inert gas, or
a mixture for a time generally of 1-24 hours.
Following this, an atmosphere containing molecular oxygen, steam and
optionally an inert gas is provided as above indicated and the temperature
is increased at a rate of about 0.5.degree. C. to 15.degree. C. per minute
to a value effective to eliminate water of hydration from the catalyst
precursor, eg. 350.degree. C. to 550.degree. C., preferably 400.degree. C.
to 450.degree. C.
The precursor is maintained at the adjusted temperature under an oxygen and
steam containing atmosphere to complete vanadium conversion to an
oxidation state of about +4.0 to about +4.5 and for the transformation of
the precursor to the active catalyst which has the formula (VO).sub.2
P.sub.2 O.sub.7 M.sub.2m P.sub.2p O.sub.y wherein M, m, p and y are as
defined above. It is essential in this step that the atmosphere contain at
least 1 vol % oxygen up to about 15 vol % oxygen, preferably at least 2
vol % oxygen and desirably 3-8 vol % oxygen. It is important to minimize
the exotherm during this process.
The catalyst may be employed as pellets, disc, flakes, wafers, or any other
convenient shape which will facilitate its use in the tubular reactors
employed for this type of vapor phase reaction. For example the catalyst
may be prepared as tablets having a hole or bore therethrough as disclosed
in U.S. Pat. No. 4,283,307 which is incorporated herein. The material can
be deposited on a carrier. Although fixed bed tubular reactors are
standard for this type of reaction, fluidized beds are frequently used for
oxidation reactions, in which case the catalyst particle size would be on
the order of about 10 to 150 microns.
The use of this class of catalyst for the partial oxidation of C.sub.4
-C.sub.10 hydrocarbons to the corresponding anhydrides is generally
recognized. They have been widely considered for the conversion of normal
C.sub.4 hydrocarbons, both the alkane, n-butane, and alkene, and alkene,
n-butane, for the production of maleic anhydride, which has a wide
commercial usage.
The oxidation of the n-C.sub.4 hydrocarbon to maleic anhydride may be
accomplished by contacting e.g. n-butane in low concentrations in oxygen
with the described catalyst. Air is entirely satisfactory as a source of
oxygen, but synthetic mixtures of oxygen and diluent gases, such as
nitrogen also may be employed. Air enriched with oxygen may be employed.
The gaseous feed stream to the standard tubular oxidation reactors normally
will contain air and about 0.5 to about 3.0 mole percent hydrocarbons such
as n-butane. About 1.0 to about 2.5 mole percent of the n-C.sub.4
hydrocarbon are satisfactory for optimum yield of product for the process
of this invention. Although higher concentrations may be employed,
explosive hazards may be encountered except in fluidized bed reactors
where concentrations of up to about 4 or 5 mole percent can be used
without explosive hazard. Lower concentrations of C.sub.4, less than about
one percent, or course, will reduce the total productivity obtained at
equivalent flow rates and thus are not normally economically employed.
The flow rate of the gaseous stream through the reactor may be varied
within rather wide limits but a preferred range of operations is at the
rate of about 10 to 300 grams of C.sub.4 per liter of catalyst per hour
and more preferably about 50 to about 250 grams of C.sub.4 per liter of
catalyst per hour. Residence times of the gas stream will normally be less
than about 4 seconds, more preferably less than about one second, and down
to a rate where less efficient operations are obtained. A preferred feed
for the catalyst of the present invention for conversion to maleic
anhydride is a n-C.sub.4 hydrocarbon comprising a predominant amount of
n-butane and more preferably at least 90 mole percent n-butane.
A variety of reactors will be found to be useful and multiple tube heat
exchanger type reactors are quite satisfactory. The tubes of such reactors
may vary in diameter from about 1/4" to about 3", and the length may be
varied from about 3 to about 18 or more feet. The oxidation reaction is an
exothermic reaction and, therefore, relatively close control of the
reaction temperature should be maintained. It is desirable to have the
surface of the reactors at a relatively constant temperature and some
medium to conduct heat from the reactors is necessary to aid temperature
control. Such media may be Woods metal, molten sulfur, mercury, molten
lead, and the like, but it has been found that eutectic salt baths are
completely satisfactory. One such salt bath is a sodium nitrate-sodium
nitrite-potassium nitrite eutectic constant temperature mixture. An
additional method of temperature control is to use a metal block reactor
whereby the metal surrounding the tube acts as a temperature regulating
body. As will be recognized by one skilled in the art, the heat exchange
medium may be kept at the proper temperature by heat exchangers and the
like. The reactor or reaction tubes may be iron, stainless steel, carbon
steel, nickel, glass tubes have excellent long life under the conditions
for the reactions described herein. Normally, the reactors contain a
preheat zone of an inert material such as 1/4' Alundum pellets, inert
ceramic balls, nickel balls or chips and the like, present at about 1/2 to
1/10 the volume of the active catalyst present.
The temperature of reaction may be varied within some limits, but normally
the reaction should be conducted at temperatures within a rather critical
range. The oxidation reaction is exothermic and once reaction is underway,
the main purpose of the salt bath or other media is to conduct heat away
from the walls of the reactor and control the reaction. Better operations
are normally obtained when the reaction temperature employed is no greater
than about 100.degree. C. above the salt bath temperature. The temperature
in the reactor, of course, will also depend to some extent upon the size
of the reactor and the C.sub.4 concentration. Under usual operating
conditions in a preferred procedure, the temperature in the center of the
reactor, measured by thermocouple, is about 365.degree. C. to about
550.degree. C. The range of temperature preferably employed in the
reactor, measured as above, should be from about 380.degree. C. to about
515.degree. C. and the best results are ordinarily obtained at
temperatures from about 380.degree. C. to about 475.degree. C. Described
another way, in terms of salt bath reactors with carbon steel reactor
tubes about 1.0" in diameter, the salt bath temperature will usually be
controlled between about 350.degree. C. to about 550.degree. C. Under
normal conditions, the temperature in the reactor ordinarily should not be
allowed to go above about 475.degree. C. for extended lengths of time
because of decreased yields and possible deactivation of the catalyst.
The reaction may be conducted at atmospheric, super atmospheric or below
atmospheric pressure. The exit pressure will be at least slightly higher
than the ambient pressure to insure a positive flow from the reaction. The
pressure of the gases must be sufficiently high to overcome the pressure
drop through the reactor.
The maleic anhydride may be recovered in a number of ways well known to
those skilled in the art. For example, the recovery may be by direct
condensation or by absorption in suitable media, with subsequent
separation and purification of the maleic anhydride.
EXAMPLE 1
Into a 12 liter round flask equipped with a mechanical stirrer, thermowell,
Dean Stark trap with a condenser and a heating mantle were charged 6452 ml
anhydrous isobutanol, 1613 ml benzyl alcohol, 70 grams of DMSO (Dimethyl
sulfoxide), 815.1 grams V.sub.2 O.sub.5, 66.9 grams of 28% Bi Hex-Cem
(this is a Bi salt of 2 ethyl hexanoic acid in a mineral spirits carrier).
About 1098 g of 100% phosphoric acid were added slowly into the reaction
mixture while stirring.
The reaction mixture was brought to ref lux which was continued overnight.
Thereafter, about 4032 ml distillate were removed and the reaction mixture
was cooled down and filtered. The product cake was divided in two and each
part was washed with about 700-1000 cc of fresh IBA (isobutyl alcohol).
The product was then dried in the oven at 110.degree. C. for 10 hours and
finally at 150.degree. C. for 16 hours. The dry cake was crushed and
calcined at 220.degree. C. for 3 hours and then at 260.degree. C. for
another 3 hours. The calcined powder was mixed with 4% graphite and was
formed into 3/16".times.3/16" tablets with a 1/16" I.D. hole struck
therethrough. The catalyst was activated in Unit A.
Unit A consists of a single 9" OD meshed tray on which the catalyst pellets
are supported. The tray was placed in a stainless steel metal unit which
was then placed in an oven which had good temperature control. The gases
entering the unit were preheated before passing through the catalyst bed.
The tray in this unit was loaded with 425 g of shaped catalyst and was
activated by the procedures described below.
A gas flow consisting by volume of 6.5% oxygen/nitrogen balance was passed
through the catalyst bed while the oven was heated from room temperature
to 275.degree. C. in 75 minutes and held for 1 hour. During this period
the catalyst bed reached the oven temperature. Thereafter, steam was
introduced into the gas stream to obtain a gas atmosphere composition by
volume of: 50% steam, 6.5% oxygen and the balance nitrogen. The oven
temperature was raised to 425.degree. C. in 38 minutes and held 10-30
minutes for the bed temperature to equilibrate with the oven temperature.
The oven temperature was then held for another 7 hours under these
conditions. At the end of this period the heating of the oven heating was
discontinued and the catalyst bed was cooled down under the same gas
mixture to 250.degree. C. Thereafter, the steam was removed, and the
catalyst bed was cooled to room temperature under dry gas containing 6.5%
oxygen/nitrogen balance. The catalyst performance is shown in Table 1.
EXAMPLE 2
A fresh catalyst precursor prepared by the procedures described in Example
1 was activated in unit A by the following procedures.
A gas flow consisting by volume of 6.5% oxygen/nitrogen balance was passed
through the catalyst bed while the oven was heated from room temperature
to 275.degree. C. in 75 minutes and held for 1 hour. During this period
the catalyst bed reached the oven temperature. Thereafter, steam was
introduced into the gas stream to obtain a gas composition by volume of:
50% steam, 6.5% oxygen and the balance nitrogen. The oven temperature was
raised to 425.degree. C. in 38 minutes and held 10-30 minutes for the bed
temperature to equilibrate with the oven temperature and the oven
temperature was held for another 3.5 hours under these conditions. The
oxygen level was then reduced to 3% O2 by volume while maintaining 50%
steam in the gas mixture, the balance being nitrogen and the oven
temperature was held for another 3.5 hours under these conditions.
Thereafter, the steam was removed, and the catalyst bed cooled to room
temperature under dry gas containing 3% oxygen/nitrogen balance by volume.
The catalyst performance is shown in Table 1.
EXAMPLE 3
A fresh catalyst prepared by the procedures described in Example 1 was
activated in unit A by the following procedures.
A gas flow consisting by volume of 21% oxygen/nitrogen balance was passed
through the catalyst bed while the oven was heated from room temperature
to 275.degree. C. in 75 minutes and held for 1 hour at that temperature.
During this period the catalyst bed reached the oven temperature.
Thereafter, steam was introduced into the gas stream to obtain a gas
composition by volume of: 50% steam, 10.5% O2 and the balance nitrogen.
The oven temperature was raised to 425.degree. C. in 38 minutes and held
10-30 minutes for the bed temperature to equilibrate with the oven
temperature. The oven temperature was held for another 1 hour under these
conditions and then the oxygen level was reduced to 6.5% oxygen while
maintaining 50% steam in the gas mixture and the balance nitrogen, the
percentages being volume percent. The oven was held at 425.degree. C.
under this gas composition for 6 hours. At the end of this period the oven
heating was stopped and the catalyst bed cooled under the same gas mixture
to 250.degree. C. Thereafter, the steam was removed, and the catalyst bed
cooled to room temperature under dry gas containing by volume 6.5%
oxygen/nitrogen balance. The catalyst performance is shown in Table 1.
EXAMPLE 4
Into a 12 liter round flask equipped with a mechanical stirrer, thermowell,
Dean Stark trap with a condenser and a heating mantle were charged 6452 ml
anhydrous isobutanol, 1613 ml benzyl alcohol, 70 grams of DMSO (Dimethyl
sulfoxide), 815.1 grams V.sub.2 O.sub.5 66.9 grams of 28% Bi Hex-Cem (this
is a Bi salt of 2 ethyl hexanoic acid in a mineral spirits carrier). About
1098 g of 100% phosphoric acid were added slowly into the reaction mixture
while stirring.
The reaction mixture was brought to ref lux which was continued overnight.
Thereafter, the reaction mixture was cooled down, 80 ml of 30% hydrogen
peroxide were added while stirring. After about 30 minutes of stirring the
reaction mixture was filtered. The solids product was then dried in the
oven at 110.degree. C. for 10 hours and finally at 150.degree. C. for 16
hours. The dry cake was crushed and calcined at 220.degree. C. for 3 hours
and then at 260.degree. C. for another 3 hours. The calcined powder was
mixed with 4% graphite and was formed into 3/16".times.3/16" tablets with
a 1/16" I.D. hole struck there through. The catalyst was activated in Unit
A by the same procedures described in Example 3. The catalyst performance
is shown in Table 1.
TABLE 1
______________________________________
Example 1 2 3 4
______________________________________
Hours 441 453 488 482
Salt .degree. C. 378 37S 381 384
Hot Spot .degree. C. 428 443 434 440
% Butane 1.29 1.30 1.31 1.30
% Conversion 79.7 79.9 79.1 79.7
% Selectivity 69.3 69.4 70.6 69.9
Wt % Yield 93.4 93.4 94.3 94.2
______________________________________
It can be seen from the above results that the catalyst prepared in
accordance with the present invention demonstrates excellent performance
for the conversion of butane to maleic anhydride.
Top